Replacing images with higher quality versions is encouraged. Category:Image requests contains a long list of files which need to be replaced, but you can replace any image with a better quality one, or mark any low quality image for replacement so that others know about it.

Here are some reasons to replace an image, or to mark an image for replacement:

Blurry

TV photo

Low quality

Watermarked

Low resolution

Incorrect aspect ratio

Screenshot of youtube video

Edited, including borders or writing

Modded content visible for no reason

The Protagonist is in view for no reason

Subject is obscured, unclear, or in the background

Screenshot was taken at night and would be clearer in the daytime

Low quality images are allowed to be uploaded, because a low quality photo of a TV is better than none at all, but should be eventually replaced by a higher quality screenshot.